This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2002-125672, filed Apr. 26, 2002, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an agent for imparting a flame retardancy to a thermoplastic resin.
2. Description of the Related Art
It is necessary for the synthetic resin used in domestic electrical appliances sold in the United States to exhibit the flame retardancy stipulated in UL-94 included in UL (Underwriters Laboratories Inc.) standards. Also, in recent years, it tends to be necessary for this standard to be satisfied in many countries in addition to the United States. Flame-retardant material satisfying the UL-94 standard tends to be used in Japan, though it is not obligatory in Japan to use the flame-retardant material satisfying this standard.
In the conventional flame-retardant, the flame retardancy is considered to be developed mainly by the three principles given below:
1) The flame retardancy is imparted to a synthetic resin by adding a halogen-based compound and a phosphoric acid-based compound to the synthetic resin. Specifically, a halogen-based compound and a phosphoric acid-based compound are added to the synthetic resin in an amount of several percent to scores of percent so as to allow these additive compounds to act as a negative catalyst relative to the combustion flame so as to stop the combustion.
2) About several percent to scores of percent of a silicone compound is added to a synthetic resin so as to allow the silicone compound to bleed on the surface of the synthetic resin under combustion. As a result, char (a carbonized layer) is formed on the surface of the synthetic resin so as to stop the combustion.
3) An inorganic salt such as magnesium hydroxide or aluminum hydroxide is added to a synthetic resin in an amount of about 30 to 40%. Since the combustion of the synthetic resin causes the added metal salt to absorb heat so as to be decomposed and to form water, the formed water cools the entire resin composition so as to stop the combustion.
However, principle 1) given above is defective in that, if a domestic electrical appliance including a synthetic resin containing a flame-retardant is discarded and combusted, the halogen compound forms dioxin and the ash formed by the combustion causes phosphoric acid, bringing about a water contamination problem. Also, in principle 2) given above, it is necessary to add a large amount of the silicone compound used as a flame-retardant to the synthetic resin. As a result, the properties inherent in the synthetic resin tend to be changed. For example, the mechanical strength of the synthetic resin tends to be lowered. Further, in principle 3) given above, it is necessary to add a large amount of the inorganic salt used as a flame-retardant to the synthetic resin, with the result that the synthetic resin tends to be hydrolyzed or the mechanical properties of the synthetic resin tend to be impaired.
As a result of extensive research into the influences of the thermal stabilizer on the thermoplastic resin, the present inventors have found that, if the thermal stability of the thermoplastic resin is highly improved, flame retardancy can be imparted to the thermoplastic resin.
The present inventors have further continued extensive research based on the finding referred to above. It has been newly found that the thermal stability of a thermoplastic resin can be improved if a small amount of a polyhydric phenol, particularly, a tannin compound, is added to the thermoplastic resin. To be more specific, it has been newly found that the decomposition temperature of the thermoplastic resin can be elevated by the addition of the polyhydric phenol so as to suppress the combustibility of the thermoplastic resin, leading to the agent of the present invention for imparting flame retardancy to the thermoplastic resin.
According to the present invention, there is provided an agent for imparting flame retardancy to a thermoplastic resin, the agent containing a polyhydric phenol as an effective component.
Additional objects and advantages of the present invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the present invention. The objects and advantages of the present invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.